Crossfield inductor for inductively heating workpieces of varying cross section



3,472,992 CROSSFIELD INDUCTOR FOR INDUCTIVELY HEATING WORKFIECES O? Oct.14, 1969 H. GEISEL ETAL VARYING CROSS SECTION Filed Feb. 12, 1968 In vantors United States Patent Office 3,472,992 Patented Oct. 14, 1969 U.S.Cl. 21910.79 5 Claims ABSTRACT OF THE DISCLOSURE In crossfield inductiveheating arrangements using a single pair of conductor bars, difficultyis experienced in obtaining uniform heating of workpieces of varyingcross section, e.g. screw blanks. This difficulty is obviated byproviding relatively narrow supplementary conductor bars adjacent to andinbetween the principal conductor bars, more nearly to conform to theoutline of the workpieces.

This invention relates to the inductive heating of electricallyconducting workpieces in a transverse magnetic field generated betweentwo parallel, adjustably spaced conductor bars.

In such inductive heating arrangements the adjustability of the parallelbars is necessary to permit the distance between the bars to be adaptedto the varying sizes of the workpieces that are to be passed through theinductor and to provide a satisfactory coupling between the heatinginductor and workpieces of different size.

However, such adjustment is difficult to effect if the workpieces thatare to be inductively heated have cross sections which differ along thelength. An example of such a workpiece is a blank for a screw or bolt.

The invention seeks to overcome this difiiculty, whereby workpieces suchas for example screw blanks may be evenly heated for a following hotworking operation.

The invention consists of a crossfield inductor for heating workpiecesof non-uniform cross section, comprising two principal conductor bars ofwidth corresponding to the entire width of the heating zone and spacedso as to accommodate the largest cross section of the said workpiece,and associated with each of the said principal conductor bars anddisposed adjacent to and inbetween the said principal conductor bars, asupplementary conductor bar of relatively narrow width.

The narrow supplementary inductor bars may be electrically connected tothe principal conductor bars, or they may be electrically insulatedtherefrom. Each principal and its associated supplementary inductor barmay be conducted to the voltage source either in parallel or in series.In a preferred arrangement of the invention, the width of thesupplementary conductor bars corresponds to the length of that part ofthe heated workpiece which has the smaller cross section, and the widthof the principal inductors is equal to the overall length of theworkpiece, to achieve even heating of the workpiece.

An embodiment of the invention is hereinafter described and illustratedin the accompanying drawing which is a perspective representation of thecross field inductor arrangement of the invention showing a workpiece inthe form of a screw blank in course of being conducted between the bars.

The width of the crossfield inductor comprising the conductor bars 1 and1 preferably corresponds to the total length of the workpiece 2 that isto be heated including the discontinuity in its cross section. As willbe understood from the drawing the conductor bars 1 and 1', are providedwith cavities 3 and 3' in conventional manner for the passagetherethrough of a liquid coolant. It is desirable to provide the sidesof the conductor bars facing away from the workpiece with cores made ofsheet metal or soft magnetic materials.-

An inductor consisting exclusively of the conductor bars 1 and 1 wouldadequately heat only the heads 2' of the blanks. In the region of theshaft of the blank, supplementary narrower conductor bars 4 and 4 arehowever, according to the invention located adjacent the inside of theconductor bars 1 and 1'.

The arrangement according to the invention is also suitable for raisingthe temperature of a desired longitudinal portion of the workpiece,'e.g. shaft, to the temperature of a head portion or to a highertemperature, and ensures that the electrical efficiency of the inductoris increased. This is due to the fact that a higher density current willflow through the conductors 4 and 4' because of their lower inductivity.Consequently, the field intensity, in this region of the inductor willbe higher and capable of adjustment by a suitable selection of thedimensions of the conductor bars 4 and 4'.

Since the power induced in the workpiece or in parts thereof isproportional to the square of the strength of the field, by selection ofdifferent field strengths in the several regions of the cross section,the desired pattern of heat distribution may be achieved in anarrangement according to the invention.

What is claimed is: Y

1. A crossfield inductor for heating workpieces of nonuniform crosssection, comprising two principal conductors bars of width correspondingto the entire width of the heating zone and spaced so as to accommodatethe largest cross section of the said workpiece, and associated'witheach of the said principal conductor bars and disposed adjacent to andinbetween the said principal conductor bars, a supplementary conductorbar of relatively narrow width.

2. A crossfield inductor according to claim 1, in which eachsupplementary conductor bar is electrically connected to its associatedprincipal conductor bars of the inductor.

3. A crossfield inductor according to claim 1, in which thesupplementary conductor bars are insulated from the main conductonbars.

4. A crossfield inductor according to claim 1, in which the width of thesupplementary conductor bars corresponds to the heating zone of the partof smaller cross section of the workpiece to be heated.

5. A crossfield inductor for uniformly heating workpieces of non-uniformcross section, comprising two principal conductor bars of widthcorresponding to the entire width of the heating zone and spaced so asto accommodate the largest cross section of the said workpieces, and asupplementary conductor bar of relatively narrow width corresponding tothe heating zone of a part of smaller cross section of the workpiece tobe heated affixed to each of said principal conductors bars, theprincipal and supplementary conductors bars substantially conforming tothe outline of said workpieces to provide uniform heating thereof.

References Cited UNITED STATES PATENTS 1,821,530 9/l93l Spire 219-l0.69X 3,251,976 5/1966 McBrien 21910.43 X

JOSEPH V. TRUHE, Primary Examiner L. H. BENDER, Assistant Examiner US.Cl. X.R.

